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Thread: high flow rate pressure regulator?

  1. #1

    Default high flow rate pressure regulator?

    My water line pressure is about 65 psi, but I need to bring it down to 55-60 psi, so as not to stress the pex tubing in my radiant floors. I installed a Cash Acme EB86U (3/4") pressure regulator, but noticed two problems: the downstream pressure will creep back up to the inlet pressure after a while, and the flow rate has been seriously impacted.

    From the specs that I've seen all pressure reducing valves, the smaller the pressure difference across the regulator, the worse the flow rate. Increasing the inlet size seems to make a difference. Maybe going to a 1" model will help? Is there any advantage to using a cartridge style, like a Watts X65B?

    Can anyone recommend a regulator that has a good flow rate for small pressure drops, and also won't creep?

    cheers, Grant.

  2. #2
    Moderator & Master Plumber hj's Avatar
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    Default Prv

    You may have a design flaw in your system. If it is a closed system your PRV should be the fill valve and it would be set at about 15 psi. The water does NOT FLOW through it. If it is an open system using the domestic water heater, you would have to give a drawing of how you handle the connections at both ends to keep the reduced pressure. And if you are reducing the pressure into the water heater, it would increase every time you open both hot and cold water valves at the same faucet. But even then the water would not flow through the valve into the grid, unless you have some "innovative" way of piping it.

  3. #3

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    It's an open system. The plumbing layout looks something like this:

    http://www.radiantcompany.com/images/muni.gif

    I've put the PRV on the cold water line that feeds the house, since 55 to 60 psi is fine for all my needs. The radiant floor section has an expansion tank, and extra pressure relief valves, so thermal expansion shouldn't be an issue.

  4. #4
    Retired Defense Industry Engineer jadnashua's Avatar
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    Pex should handle the temp of a normal WH at 65#. The max pressure does drop with temperature on pex, but normal radiant flooring heating temps shouldn't be an issue.

    I hope all of your controls, pumps, etc. are bronze or SS, or, they won't last. The dissolved oxygen in the incoming water will eat them up if not.
    Last edited by jadnashua; 07-07-2009 at 03:11 PM.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  5. #5
    Moderator & Master Plumber hj's Avatar
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    Default heat

    Your analysis is faulty. The flow rate in your system has NOTHING to do with the pressure OR the pressure reducing valve. The pump creates the flow and it is independent of outside forces. IF you have a flow problem it is in the system itself. It should make no difference whether the pressure is 12 psi, which would be normal, or 100 psi, the operation should be the same.

  6. #6
    Plunger/TurdPuncher kingsotall's Avatar
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    Where are you getting info about stressing the tubing in the floor┐
    I just post cuz I like to see my avatar.

  7. #7

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    I'm seeing the low flow rate not on the radiant floor circuit, but on the flow coming out of the taps. In fact, the radiant floor isn't even active right now, as the temps are pretty moderate here. I only installed the prv recently, and noticed an immediate drop in the flow rate. There's also the question of pressure creep downstream of the valve - the static pressure slowly rises over time to the incoming pressure.

    The radiant floor guys recommended running at 55 to 60 psi, at around 130 degrees. I could probably run at 65 psi, though I'll have to adjust the pressure relief valve on the radiant circuit. I wanted an upstream pressure regulator though, in case the city pressure spikes. I don't want the pressure relief valve in the radiant circuit to have to release water to control the pressure in the system - that should be for emergencies only.

    And yes, the pumps are stainless.

  8. #8
    Engineer garyl53's Avatar
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    If the PSI is rising above the PRV initial setting pressure I think it must be caused by either a defective PRV or a misplaced, too small or defective expansion tank which is not handling the thermal expansion properly. Also I believe it is possible to use two PRVs in series to keep the individual pressure drops lower so you can keep the flow rate higher.
    G

  9. #9

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    It's definitely not thermal expansion - I see the pressure increase even when there's no demand for hot water, and the heater is an on demand type.

    As for putting the prvs in series, to minimize the pressure drop across them, I think that's exactly the wrong idea, as the flow rate is proportional to the pressure difference - small pressure drops result in low flow rates, which is my problem to start with.

  10. #10
    Moderator & Master Plumber hj's Avatar
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    Default Prv

    PRessure creep is an indication of a bad, or sticking, PRV valve. And if it is stuck, then it might also not be opening to give full flow.

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    Plumber Cass's Avatar
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    You may have a bad PRV....like hj said...I am leaning that way

  12. #12
    Moderator & Master Plumber hj's Avatar
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    Default pressure

    Pressure creep is ALWAYS a malfunctioning PRV, when it is not thermal expansion. It can be caused by something sticking on the seat preventing proper closure, or a sticking mechanism which does the same thing. But a sticking mechanism can also NOT open fully restricting the available flow. A pressure gauge will quickly indicate it, since the pressure will DROP when a faucet is opened if the valve is sticking. PRoper operation will give almost no change in the indicated pressure whether the faucets are open or closed.

  13. #13
    Plumber jimbo's Avatar
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    Note that in the charts, the lowest Δ P mentioned is 10 PSI. At any given Δ P the higher the flow rate, the larger the pressure variation. So you are operating at the fringe of the envelope.


  14. #14

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    Thanks for all of the suggestions. I'll try exchanging the valve (it was brand new) for another 3/4", and if that doesn't work, try a 1".

    Does the water meter at the street also have a pressure regulator? If so, I wonder if I can increase the pressure there, so as to achieve a large pressure drop across my prv.

  15. #15
    Moderator & Master Plumber hj's Avatar
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    Default Prv

    There should not be one at the meter, but if there is adjust it to the proper pressure and eliminate the one you are installing.

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